Lycoming IO-320-A1A Operator's Manual page 43

SECTION 4
PERIODIC INSPECTIONS
1. DAILY PRE-FLIGHT.
2. 25-HOUR INSPECTION.
a. Lubrication System (Engines Equipped with Oil Pressure Screen)-
Change the oil at least every four (4) months even if the engine has not accumulated 25
hours since the last oil change.
3. 50-HOUR INSPECTION.
a. Ignition System –
LYCOMING OPERATOR'S MANUAL
NOTE
IO-320 SERIES